Purpose: In order to improve the pathophysiologic understanding of visual changes observed in astronauts, we aimed to use quantitative MRI to measure anatomic and physiologic responses during a ground-based spaceflight analogue (head down tilt, HDT) combined with increased ambient carbon dioxide (CO2). Methods: Six healthy, male subjects participated in the double-blinded, randomized cross-over design study with two conditions: 26.5 h of -12° HDT with ambient air and with 0.5% CO2, both followed by 2.5 h exposure to 3% CO2. Volume and mean diffusivity quantification of the lateral ventricle and phase-contrast flow sequences of the internal carotid arteries and cerebral aqueduct were acquired at 3T. Results: Compared to supine baseline, HDT (ambient air) resulted in an increase in lateral ventricular volume (P=0.03). Cerebral blood flow, however, decreased with HDT in the presence of either ambient air or 0.5% CO2 (P=0.002 and P=0.01 respectively); this was partially reversed by acute 3% CO2 exposure. Following HDT (ambient air), exposure to 3% CO2 increased aqueductal cerebral spinal fluid velocity amplitude (P=0.01) and lateral ventricle CSF mean diffusivity (P=0.001). Conclusion: HDT causes alterations in cranial anatomy and physiology that are associated with decreased craniospinal compliance. Brief exposure to 3% CO2 augments CSF pulsatility within the cerebral aqueduct and lateral ventricles.
- head down tilt
- carbon dioxide
- intracranial hypertension
- Copyright © 2016, Journal of Applied Physiology